How did you install? From cd then update? The installation probably went fine, but the update might have been an issue. There are some problems with the repositories right now.
Check here http://ubuntuforums.org/showthread.php?p=3784432
Regardless, I don't think you should have any firewall problems related to this. You should, however, run a firewall (you probably already are). Use synaptic in the System > Administration menu to get/install firestarter. It has a good interface for beginners.